1. Field of the Invention
The present invention relates to a kind of organic thin film transistor (to be abbreviated as OTFT hereinafter) and a manufacturing method thereof.
2. Description of the Related Art
In recent years, the performances of the OTFT have been continuously improved. The carrier mobility of some transistors made of such organic materials as Pentacene, Oligothiophene, Tetracene and so on is over 1 cm2/V.s, therefore, these transistors are potential in such practical applications as active matrix display, flexural integrated circuit (to be abbreviated as IC hereinafter) and so on. Because the organic semiconductor materials are sensitive to some chemical solvents generally used in the traditional process of photolithography, it is comparatively difficult to deal with this kind of device's fine finish. At present, the method of setting the organic semiconductor layer above the source/drain electrode (generally referred to bottom electrode OTFT, please see FIG. 1) is usually adopted to avoid the problem of fine finish to the device's FIGURE. But this kind of device's channel on-state current is lower than that of the device whose organic semiconductor layer is set under the source/drain electrode (referred to top electrode OTFT, please see FIG. 2). In a word, form the point view of structure, the top electrode device is superior to the bottom electrode one (please turn to FIGS. 3 and 4 to see the comparison). In addition, by far threshold voltage of the OTFT is a little higher. The threshold voltage can be affected by many factors, such as, for example, the interface behavior of the organic layer and the insulation layer, the contact performance between the source/drain electrode and the organic semiconductor, etc. The available method of effectively reducing the threshold voltage is to reduce the thickness of the insulation film or to use the material with high dielectric constant (e.g. barium titanate, BZT) as the insulation layer (C. D. Dimitrakopoulos et al Science 283, 822, 1999). Unfortunately, all the two methods increase the leakage current between the gate electrode and the source electrode, between the gate electrode and the drain electrode. The main reason is that the material with high dielectric constant is poor in insulatibity. In recent years, the Chinese Patent Application CN 1293825A discloses a kind of transistor (including the inorganic and organic ones) having a upstanding configuration, and the Jackson research group in Pennsylvanian State University also discloses a method for simplifying the OTFT structure (Appl. Phys. Lett. 2000, 76: 1692-1694). However, neither of the above two methods can solve the above-mentioned problems.